Thermal printers of the type with which the present disclosure is concerned have been known for many years. They operate with a supply of tape arranged to receive an image and a means for transferring the image onto the tape. In one form, a tape holding case or cassette holds a supply of image receiving tape and a supply of an image transfer ribbon, the image receiving tape and transfer ribbon being passed in overlap through a printing zone of the printing device. An early printing device operating with a tape holding case of this type is described for example in EP-A-0267890 (Varitronics, Inc.). Other printing devices have been made in which letters are transferred to an image receiving tape by a dry lettering or dry film impression process. In all of these printing devices, the construction of the image receiving tape is substantially the same. That is, it comprises an upper layer for receiving an image which is secured to a releasable backing layer by a layer of adhesive. Once an image or message has been printed on the tape, it is desired to cut off that portion of the tape to enable it to be used as a label. For this purpose, it is necessary to remove the releasable backing layer from the upper layer to enable the upper layer to be secured to a surface by means of the adhesive layer. In EP-A-0267890 scissors are used to cut off the tape.
In a further printing device, described for example in EP-A-0487313 (Esselte Dymo N.V.), a tape holding case holds a supply of image receiving tape and a supply of image transfer ribbon, the image receiving tape having the same construction as described above with reference to EP-A-0267890. In this device, the cassette includes a feed roller which is rotatably mounted and which cooperates with an output roller of a printing device into which the cassette is inserted to feed the image receiving tape out of the printing device after printing has taken place. After the tape has been fed out of the cassette, the printed portion of the tape is cut off by a cutting mechanism located outside the cassette boundary.
In both of these devices, printing is carried out at a print location defined by a thermal print head and a platen against which the print head presses the image receiving tape and image transfer ribbon during printing. The image receiving tape is then fed past the print location by the feed mechanism comprising the feed roller of the cassette and the output roller of the printing device to a cutting mechanism located outside the cassette boundary.
During a printing operation of the type described above the tape is fed in a forwards direction, such that the tape moves from the print location towards the cutting mechanism and eventually outputs the tape printer. However, there may also be a requirement to feed the tape in a reverse direction, such that the tape moved from the cutting mechanism back towards the print location.
EP-A-0573188 (Esselte Dymo N.V.) describes a printing apparatus that is capable of printing an image on an image receiving tape which is wider than the print head. It does this by printing a lower part of a label on a wide image receiving tape, then rewinding the image receiving tape and raising the print head, and then printing an upper part of a label above the lower part. The tape is rewound using feed rollers and the rewound tape is fed back into the tape cassette. As this is rewinding the tape in order to repeatedly print over the same region of tape, the leading edge of the tape is never rewound further back than its initial location at the cutting mechanism. If the tape were to be rewound further, past the location of the cutting mechanism, then there is a risk that the tape would not relocate correctly in the region of the cutting means when it was subsequently fed forwards. This could result in the tape becoming jammed in the printer.
EP-A-0641663 (Brother) describes a tape printer which reverses the feeding direction of the tape. The tape can be rewound in order to allow the same part of the tape to be repeatedly printed. This is done in order to allow frames and embellishments to be added to a label, to repeatedly print the same text to produce a bold font, or to allow multicolour printing. In addition, the tape may be rewound to reduce the margins caused by the distance between the cutting mechanism and the print head. During a rewinding operation the platen and the print head are separated, and the tape is rewound back onto the tape spool whilst being fed by feed rollers located in a downstream direction of the print location. However, the tape can only be rewound a maximum distance, such that the leading edge of the tape is still located between the feed rollers. If the tape were to be rewound further, then it could not be subsequently fed forwards by the feed rollers, and the tape would become jammed in the printer. This limit on the rewind distance means that the margins on the printed label can only be reduced to a minimum size, corresponding to the distance between the feed rollers and the printing head.
It can therefore be seen that known printers that rewind the image receiving tape are limited in the extent to which the tape may be rewound, due to the risk of the tape becoming jammed when it is subsequently fed forwards. There is therefore a requirement for a printing apparatus that can reliably rewind the tape such that the leading edge is close to the print location, without risking subsequent jamming.